1. Field of the Invention
The present invention relates to water jet processing methods of cutting a platelike workpiece made of a relatively brittler material by producing a jet of high-pressure processing water directed to the workpiece. In particular, the invention relates to such a water jet processing method in the case where cutting lines are intersected with each other.
2. Description of the Related Art
Substrates mounted thereon with e.g. a semiconductor device are frequently made of a brittle material such as glass epoxy, glass composite or the like. The glass epoxy is made by impregnating an epoxy resin into a stack of glass fiber-made fabrics. The glass composite is made by impregnating an epoxy resin into a stack of cut and trimmed glass fibers. Such brittle substrates are obtained by cutting one large material in a lattice pattern. The water jet mentioned above in which high-pressure processing water is jetted to a workpiece is used as a cutting method in some cases. See Japanese Patent Laid-open No. Hei 5-253843.
Referring to FIGS. 6A, 6B and 6C, when a substrate material is cut in a lattice pattern by water jet, there arises a situation as below. A linear cut line (the second cut line) 2a is made to orthogonally intersect another linear cut line (the first cut line) 1a for cutting, the first cut line having initially been cut to extend in one direction. The substrate is previously formed with predetermined cutting lines each serving as an index for a corresponding cut line.
FIG. 7 illustrates a state where water jet is directed from a traveling nozzle 13 to a substrate 5 to form a second cut line 2a toward a first cut line 1a, a shaded portion being a cut portion of a material. As shown in the figure, a front edge 2b of the second cut line 2a against which the water jet collides is formed to have a delay rearward of the advancing direction as it goes toward the back (underside) from the front surface subjected to the jet. In short, “delay-inclination” is occurring. The second cut line 2a reaches the first cut line 1a while forming such delay-inclination. In that instant, a phenomenon arises in which most pressure of the water jet cutting the material escapes at one burst toward the first cut line 1a which is a cavity. This phenomenon causes an insufficient cut area, i.e., insufficient processing area 2c under the delay-inclination. This leads to a problem in that projections 9 are formed to narrow the second cut line 2a as shown in FIGS. 5A and 8B. The insufficient processing area 2c is more liable to occur as the travel speed of the nozzle 13 is higher and the angle θ of the delay-inclination shown in FIG. 7 becomes larger to more increase the degree of the delay-inclination.
At the time when the escape of water jet mentioned above occurs, the first cut line 1a and the second cut line 2a intersect with each other in a T-shape as shown in FIG. 6B. In order to subsequently form the second cut line 2a from such a position, the water jet that has traversed the first cut line 1a orthogonally collides against a wall (a portion indicated with reference numeral 8 of FIG. 6B) of the material to be cut therefrom and then the second cut line is made to crisscross intersect the first cut line 1a. However, when the collision occurs, the processing water colliding against and bouncing off the wall hits the vicinity of the opening of the already cut second cut line 2a with respect to the first cut line 1a. Thus, a disadvantage occurs that inadvertent processing is done such as damage to the vicinity of the opening (e.g., a portion surrounded by a broken line of FIG. 8A).
As described above, if cutting is performed by water jet to cause the second cut line to intersect the first cut line, a disadvantage occurs that an insufficient processing area is formed on the underside of the workpiece and in the front of the intersection of the second cut line with the first cut line and the vicinity of the opening to the first cut line is unnecessarily damaged. These disadvantages tend to be more remarkable as the travel speed of the water jet is higher.